The present invention relates to a fuel piping structure for a diesel engine.
The following structures are each known as a fuel circuit for supplying fuel to a fuel injection nozzle located in each cylinder of a diesel engine and for returning excess fuel into a fuel tank.
(1) An Engine of a Separate Cylinder Head Structure
A fuel manifold is attached on side faces of separated cylinder heads, and fuel is supplied from the fuel manifold to each fuel injection nozzle while excess fuel is returned. FIG. 7 schematically shows an example of a fuel circuit in a six-cylinder in-line diesel engine of a separate cylinder head structure, in which fuel injection nozzles 22 are respectively placed in six cylinder heads 21 each independently provided for each cylinder. A front side fuel manifold 23 is fastened to side faces of No. 1 to No. 3 cylinder heads 21, and a rear side fuel manifold 24 is fastened to side faces of No. 4 to No. 6 cylinder heads 21, out of the aforesaid cylinder heads 21. In FIG. 7, the front side fuel manifold 23 and the rear side fuel manifold 24 are shown by the diagonally shaded areas.
A fuel supply bore 23a, fuel supply bores 23b branching from the fuel supply bore 23a toward the respective injection nozzles 22, a fuel return bore 23c, and fuel return bores 23d branching form the fuel return bore 23c toward the respective injection nozzles 22 are provided inside the front side fuel manifold 23. The fuel supply bore 23b and the fuel return bore 23d are respectively connected to a fuel supply bore 21a and a fuel return bore 21b provided in each of the cylinder head 21. On the contact faces of each cylinder head 21 and the front side fuel manifold 23, O-rings not shown are respectively attached between the contact portions of the fuel supply bore 23b and the fuel supply bore 21a, and between the contact portions of the fuel return bore 21b and the fuel return bore 23d. Further, the relationships between the fuel circuit provided inside the rear side fuel manifold 24 and the cylinder heads 21 are identical to the case of the front side fuel manifold 23, thus omitting the explanation thereof.
An intake manifold 25 is also fastened to the side face of each cylinder head 21. As a result, a fuel supply line 29, which runs from a fuel tank 26 by way of a fuel filter 27 and a fuel pump 28, branches in the longitudinal direction of the paper face of FIG. 7, and goes around a front end and a rear end of the intake manifold 25 to be connected to a front end of the front side fuel manifold 23 and a rear end of the rear side fuel manifold 24 respectively. Fuel return lines, which are connected to the front end of the front side fuel manifold 23 and the rear end of the rear side fuel manifold 24 respectively, are combined into one fuel return line 30, and thereafter it is connected to the fuel tank 26 via a fuel cooler 31.
(2) An Engine with an Integral-type of Cylinder Head Structure
In this case, a fuel manifold as in the above item (1) is adopted, or common-supply-and-return-fuel-lines which run through each cylinder are provided inside a cylinder head, thereby directly connecting external lines to the fuel manifold or the common fuel lines.
(3) In a fluid circuit for an engine cylinder head, which is proposed by the present inventor and disclosed in Japanese Patent Application Laid-open No. 6-207565, an engine with a separate cylinder head structure is used. However, the fuel manifold is not used, and a fuel circuit is formed by connecting fuel supply lines each provided inside a rocker housing of each cylinder, and fuel return lines, with pipes respectively.
However, the above prior arts have the following disadvantages.
(1) The Disadvantage Common to the Respective Kinds of Engine Explained in the Prior Art.
Since the fuel circuit is not cooled by the fluid (for example, air, water, and the like) inside the engine, the temperature of fuel (specifically, excess fuel) cannot be reduced. Accordingly, in order to cool the fuel, a fuel cooler of large capacity has to be additionally placed.
(2) The Disadvantage Regarding the Fuel Manifold
A fuel manifold is generally manufactured by extrusion molding of aluminum material (plastic processing), and an O-ring is incorporated in order to prevent fuel leak at the contact portions of the fuel manifold and the cylinder head. However, since the fuel manifold is long, it is difficult to secure flatness on the surface scaled by the O-ring, and the O-ring is easy to come off during assembly. Consequently, there is the disadvantage of fuel seal being less reliable.
(3) The Disadvantage Regarding the Common Fuel Line Provided Inside the Cylinder Head
This is used in an engine with an integral-type of cylinder head structure, but if this is used in a large-sized engine with a separate cylinder head structure which is generally adopted, it is extremely difficult to provide a common fuel line, which runs through each cylinder, inside the cylinder head.
(4) The Disadvantage Regarding Japanese Patent Application Laid-open No. 6-207565
The art disclosed in Japanese Patent Application Laid-open No. 6-207565 is one of the means for overcoming the above disadvantages. However, since a fuel cooling function is not included in the art, it is necessary to additionally provide a fuel cooler of large capacity in order to cool fuel.
In view of the above disadvantage of the above prior art, the present invention is made, and its object is to provide a fuel piping structure for a diesel engine capable of cooling fuel (including excess fuel) flowing through a fuel circuit of a fuel injection system, and capable of making the fuel circuit compact in size.
A fuel piping structure for a diesel engine according to the present invention is a fuel piping structure for a diesel engine in which a fuel circuit is provided between a fuel lank and fuel injection nozzles each for each cylinder head, and is characterized in that
a part of the fuel circuit is formed inside an intake manifold.
According to the above configuration, since a part of the fuel circuit is formed inside the intake manifold, that is, the intake manifold is used for a dual purpose, the fuel manifold conventionally used becomes unnecessary. As a result, a component configuration and piping structure on the side of the cylinder head, to which the intake manifold is mounted, are simplified, and thus the engine can be made compact in size.
Further, in the fuel piping, structure, the part of the fuel circuit may be a part of a fuel return circuit running from the fuel injection nozzles to the fuel tank.
According to the above structure, since a part of the fuel return circuit running from the fuel injection nozzles to the fuel tank is formed inside the intake manifold, excess fuel is cooled by air flowing through the intake manifold. The cooling effect becomes especially large when an engine with a system in which air compressed by a supercharger is cooled by means of an after-cooler. Since excess amount of fuel (specifically, excess fuel) which is pressurized to he heated to a high temperature is efficiently cooled inside the intake manifold when returning to the tank, the fuel cooler, which is conventionally indispensable, can be withdrawn from service or downsized. Further, the temperature of the fuel tank decreases with falling temperature of the excess fuel, thus improving, safety.
Furthermore, in the fuel piping structure for the diesel engine, the part of the fuel circuit may be a part of a fuel supply circuit running from the fuel tank to the fuel injection nozzles.
According to the above configuration, since a part of the fuel supply circuit is formed inside the intake manifold, the fuel manifold conventionally used becomes unnecessary. As a result, the component configuration on the side of the cylinder head, to which the intake manifold is mounted, can be simplified. Further, since the fuel supply piping structure is simplified, a useless part of the piping volume is eliminated, and load on the fuel pump can be reduced.
Further, in the fuel piping structure for the diesel engine, at least one of the part of the fuel supply circuit may be formed inside the intake manifold, and
fuel supply lines, which are provided between the fuel tank and the part of the fuel supply circuit at least one of which is formed, may be connected to approximately center portions in longitudinal directions of the part of the fuel supply circuit at least one of which is formed.
According to the above configuration, the fuel piping provided between the fuel tank and the intake manifold can be drastically shortened to be placed compared to the prior art. As a result, useless volume of the fuel line can be eliminated, and the fuel line can be simplified in shape and downsized. Further, significant imbalance is eliminated and the balance is achieved in the distances from the connection portion of the fuel circuit with the intake manifold to the fuel injection nozzles, thereby reducing variations in the amount of injection in each cylinder, and improving the engine performance.
Furthermore, in the fuel piping structure, at least one of the following: longitudinal portions of the intake manifold, which are in the part of the fuel supply circuit; and longitudinal portions of the intake manifold, which are in the part of the fuel return circuit, may be machined and formed from both ends of the intake manifold in the longitudinal direction thereof.
According to the above configuration, the fuel supply circuit and/or the fuel return circuit are/is separately machined from both ends of the intake manifold in the longitudinal direction thereof, thus making a necessary stroke of a work machine smaller, facilitating machining, and finishing machining, in a short time. In addition, each fuel circuit can be shortened, and a useless volume of the fuel circuit can be eliminated, thus reducing load on the fuel pump. In addition, variations in the amount of injection in each cylinder are reduced, and the engine performance can be improved.
Further, in the fuel piping structure, an intake manifold gasket, which is attached between contact faces of the intake manifold and the cylinder head, and has fuel holes for connecting the fuel circuits respectively formed in the intake manifold and the cylinder head, may be included, and each of the fuel holes may be formed by a rubber seal which is integrally fixed to the intake manifold gasket.
According to the above structure, the rubber seal is added to the conventional air scaling intake manifold gasket to be integrally fixed thereto for connecting the fuel circuit. As a result, fuel leakage can be surely prevented, and the falling off of an O-ring, is eliminated, which is conventionally the disadvantage when the fuel manifold is mounted, and easiness in assembly can be increased.